Bioethanol is expected to be a renewable resource that is produced by biomass. Moreover, since carbon dioxide that is produced by combustion of bioethanol is carbon neutral, increased use of bioethanol is considered to suppress increase of carbon dioxide, which is a main cause of the global warming.
Bioethanol is obtained by fermenting biomass and distilling and purifying ethanol. It is necessary to produce much alcohol from saccharified solutions for increasing the yield of bioethanol. Since the yeasts generally used in the process of bioethanol production cannot convert pentose such as xylose and arabinose into alcohol, only hexose has been used as raw materials for fermentation.
Typical biomass is reported to contain 35-45% of cellulose, 25-40% of hemicellulose, and 15-30% of lignin, though the contents vary according to raw materials. Therefore, use of hemicellulose, which mainly contains the pentose xylose, but not only cellulose, which is a polymer of hexose, as a substrate should lead to effective ethanol production.
Xylose is reported to be the second abundant sugar in biomass next to glucose and it is an important object in bioethanol production to use pentose effectively.
Techniques for using xylose, even at a little amount, by imparting the ability to utilize xylose by genetic recombination, using microorganism that produces ethanol from xylose, or the like have been so far disclosed.
Patent Literature 1 discloses an invention involving converting xylose (C5) into xylulose by introducing a gene having the xylose transporter activity into a host cell to incorporate it in the pentose phosphate pathway of the glycolysis and use it for fermentation.
Patent Literature 2 discloses a technique for producing alcohol with yeast provided with an arabinose transporter. This involves incorporation of arabinose (C5) via arabitol and xylulose in the pentose phosphate pathway in the glycolysis to use it for fermentation, similar to the invention of Patent Literature 1.
Non-Patent Literature 1 discloses provision of xylose utilization ability by incorporating a xylose utilization gene derived from Escherichia coli in Zymomonas. 
Non-Patent Literature 2 describes production of ethanol from xylose by yeast in the genus Pichia. 